One tip I've learned is always to come in my girlfriend's mouth. As I have to point out to her every single time while she's complaining about the taste, it saves her washing the sheets as often.
To be honest, she used so much bleach, she was sick after inhaling the fumes. I felt really sorry for her because it was just one more thing to add to the list of things she had to clean up.
The other thing to do is make sure the standards don't drop. I noticed a few months back that my girlfriend was not cleaning the toilet as often, putting bleach down it less frequently, replacing the toilet duck less diligently. Now these are all easy things to do and I could have done them...
My girlfriend won't let me do any of the housework. She insists on doing it all while I am out or otherwise occupied. She says this is because she wants the place to be nice for me when I get home from work. I remember how upset she was one day when she was ill and couldn't do the washing-up...